1. Field of the Invention
The present invention relates to a method of manufacturing a semiconductor device, and more particularly to a method of forming a tungsten gate electrode.
2. Description of the Related Art
In general, a polysilicon layer is used for a gate electrode material of a MOSFET. However, as high integration of a semiconductor device, the line width of the gate electrode is significantly reduced. Therefore, in case of a polysilicon gate electrode, it is difficult to obtain low resistivity required for the high integration device. Accordingly, a tungsten layer has been researched as the gate electrode material, recently.
In case of a tungsten gate electrode, gate re-oxidation process is generally performed after forming a tungsten gate electrode, for improving the reliability of a gate insulating layer. However, when performing the gate re-oxidation process, the side wall of a tungsten layer 5 is excessively oxidized due to its fast oxidation rate, to occur abnormal oxidation of the tungsten layer 5, as shown in FIG. 1, thereby deteriorating properties and reliability of a device. In FIG. 1, reference numbers 1, 2, 3 and 4 indicate a semiconductor substrate, a gate oxide layer, a polysilicon layer and a diffusion barrier layer, respectively. Furthermore, reference numbers 6 and 7 indicate a mask pattern used for etch barrier and a thermal oxidation layer grown by abnormal oxidation, respectively.
To solve the above problem, a method of forming a tungsten gate electrode using a spacer, is suggested. Referring to FIG. 2 when performing etch process to form a gate electrode, the tungsten layer 5 and the diffusion barrier layer 4 are etched and a spacer 8 is then formed on the side wall of the etched tungsten layer 5 and diffusion barrier layer 4. Therefore, when performing subsequent gate re-oxidation process, abnormal oxidation is not occurred on side wall of the tungsten layer 5.
Thereafter, as not shown in FIG. 2, the polysilicon layer 3 and the gate oxide layer 2 are etched to form a gate electrode. Next, LDD ion implantation and gate re-oxidation processes are performed, respectively.
As described above, when performing gate re-oxidation process, abnormal oxidation is not occurred on side of the tungsten layer 5 by the spacer 8. However, since the width of the gate electrode increases due to the spacer 6, it is difficult to apply high integration semiconductor device required for a gate electrode with fine line width.